The official, who spoke to ABC News on condition of anonymity to preview the president's speech at West Point this evening, said "there's going to be an initiative of Afghans taking responsibility in certain geographic areas, certainly during this term."

That will allow, the official said, a "thinning out" of the estimated 100,000 US forces in the country by then -- some 70,000 in Afghanistan currently, with the president about to send 30,000 more -- "by the end of the president's first term."

The president's strategy will include accelerated training of Afghan forces, an emphasis on security for population centers, and "bringing security to more areas of the country," the official said.

That, he said, will "bolster the confidence of the Afghan people in US resolve," which will lead to more Afghans joining the army and police.

The official rejected the argument that off-ramps or timelines for US withdrawal would undermine that confidence, saying that military surges in general are for specific periods of time and not open-ended.

The goal of the president's strategy has not changed, he said: "disrupting, dismantling and defeating al Qaeda."

In Pakistan, that goal means degrading extremist forces who threaten the government, keeping the government stable, ensuring the security of its nuclear weapons, and reducing tensions with India.

In Afghanistan, the official said, that goal means reversing the momentum of the Taliban so the Afghans can govern themselves.

The Afghan government will need to take on greater responsibility for its own security, and the US will focus on key minstries and on local governments, he said.

Earlier this year, approximately 320 US civilian personnel were in Afghanistan. By the first quarter of 2010, the official said, the number will be closer to a thousand. Around sixty percent of the new civilian forces will be based outside Kabul.